This invention relates to an alternator for an automotive vehicle.
Due to downsizing, weight reduction, and power increase of recent engines, electric devices or accessories installed on the engine are subjected to severe vibrations. Furthermore, for the purpose of reducing an aerodynamic resistance of a traveling vehicle, the vehicle body employs a slant nose shape. Meanwhile, the number of components to be installed in an engine room is increasing recently. Furthermore, from the need of securing a comfortable compartment space, the space available for the engine is becoming smaller. Under such environments, the automotive alternators tend to be subjected to higher ambient temperatures. On the other hand, seeking comfortableness and safety in the vehicle necessarily increases the electric load of various electric devices. The automotive alternators are thus required to generate a large amount of electric power and inevitably generate a great amount of heat. A rectifying device of the alternator includes rectifying elements (e.g., diodes) which have the tendency of being kept at high temperatures. From the reasons described above, the recent automotive alternators are severely required to assure reliable anti-vibration properties and excellent cooling ability.
U.S. Pat. No. 5,828,564 discloses a rectifying element whose metallic base side wall is securely fixed into a receiving recess of a radiator fin. A heat conductive member is interposed between a metallic base bottom of the rectifying element and a receiving recess bottom. This arrangement is advantageous in that no soldering operation is required and accordingly the manufacturing cost can be reduced.
On the other hand, Japanese Patent Application Laid-open No. 11-164538(1999) discloses a rectifying device including a large-diameter fin and a small-diameter fin arranged in an overlapped relationship, according to which the small-diameter fin is disposed closely to a cooling air inlet port and rectifying elements are fixedly driven or implanted in receiving holes of this radiator fin.
When these conventional rectifying devices are subjected to severe vibrations of an automotive vehicle, there is the possibility that any crack may appear and grow from the receiving recess or hole. Furthermore, repetitive thermal stresses applied thereon will loosen the rectifying element out of the receiving recess or hole. This will lead to abnormal power generation from the alternator. Especially, the small-diameter fin of the rectifying device is serious about this problem because the rectifying elements are disposed closely with each other due to a small surface area of the fin. Furthermore, adding the heat conductive member will increase the total number of constituent parts of the alternator and accordingly increase the manufacturing costs.
Furthermore, U.S. Pat. No. 6,198,187 discloses a heat sink with a plurality of fins extending in radial directions.
However, according to this prior art, each rectifying element is fixed to the fin by soldering. If this conventional rectifying device is used under recent high-temperature environments of the automotive vehicle, the soldered portion may melt or thermally fatigue. In this case, replacing the soldering by the above-described engagement is difficult because forming or opening the receiving recesses or holes will sacrifice many of fins extending in radial directions. Furthermore, a larger-diameter heat sink having no radial fins has a smaller radiation area compared with the small-diameter heat sink. Rectifying elements are required to possess excellent heat durability. The cost will increase. In this case, it may be possible to let the large-diameter fin serve as a frame (i.e., integrate the large-diameter fin with the frame), so as to substantially increase the radiation area. However, in this case, lead portions of each rectifying device need to be welded after the rectifying device is installed in the frame. In other words, wiring connection cannot be accomplished by the rectifying device alone before the rectifying device is assembled with the frame. In general, the frames of alternators are differentiated in the shape of stay for adjustment to various types of engines. Hence, the work of accomplishing a rectifying circuit, when performed after the rectifying device is assembled with the frame, needs to match with the various types of frames. Thus, the manufacturing process will become complicated. The manufacturing costs will increase. In the practical use of automotive alternators, damage or failure of the alternator cannot be fixed by simply replacing the damaged or failed rectifying device with a new one. In other words, a frame integrated with the rectifying device needs to be replaced together. Users will need to absorb the cost of the frame replaced together with the rectifying device.
In view of the above-described problems, the present invention has an object to provide an alternator for an automotive vehicle which is capable of assuring excellent anti-vibration properties and cooling ability without increasing costs.
In order to accomplish the above and other related objects, the present invention provides an alternator for an automotive vehicle, including a rotor, a stator disposed in an opposed relationship with the rotor, a frame supporting the rotor and the stator, a rectifying device for converting alternating-current output of the stator into direct-current output, and a cooling fan for introducing cooling air from an outside via the rectifying device. The rectifying device, disposed inside the alternator, includes a small-diameter fin and a large-diameter fin having mutually different polarities and each serving as a cooling member as well as an electric conductive member for a plurality of rectifying elements fixed in receiving holes of respective fins, and a terminal base forming a rectifying circuit of the rectifying elements. The small-diameter fin and the large-diameter fin, each extending in a direction normal to an axial direction of the rotor, are disposed at both sides of the terminal base so as to be overlapped in the axial direction of the rotor. The small-diameter fin is disposed far from the rotor compared with the large-diameter fin. And, the small-diameter fin is provided with a plurality of independent ribs each protruding in the axial direction of the rotor and extending in a radial direction of the rotor from or along an opening periphery of the receiving hole of the rectifying element.
With this arrangement, the rigidity of the small-diameter fin can be enhanced specifically in the vicinity of the receiving hole of the rectifying element. This makes it possible to prevent the small-diameter fin from cracking and also prevent the rectifying element from being loosened. The automotive alternator of this invention assures excellent anti-vibration properties as well as excellent heat durability. Furthermore, the ribs are independent from each other and extend in radial directions. When the cooling fan is rotating, the cooling air introduced from the outside can flow smoothly along the rib surfaces with a smaller flow resistance. The cooling ability of the small-diameter fin can be improved. Furthermore, the terminal base, the small-diameter cooling fin, the large-diameter cooling fin, and the rectifying elements can constitute an independent rectifying circuit in the rectifying device. Compared with a conventional alternator including a frame integrated with a large-diameter fin, it becomes possible to simplify the manufacturing process of the alternator. Thus, the manufacturing cost can be reduced. In an event that any damage or failure occurs in the rectifying device, the repair of the alternator can be easily accomplished by replacing the damaged or failed rectifying device with a new one. Thus, the repair or maintenance cost can be decreased.
Preferably, the ribs are configured into wavy shape. With this arrangement, the heat radiation or heat exchange surface of each rig is increased. The cooling ability of the small-diameter fin can be improved. Furthermore, the wavy rib brings the effect of enhancing the rigidity of the small-diameter fin.
Preferably, the small-diameter fin has a plurality of through holes extending in the axial direction of the rotor for allowing the cooling air to pass and flow toward the large-diameter fin positioned closely to the rotor. With this arrangement, the cooling air can be effectively used for cooling both the small-diameter fin and the large-diameter fin.
Preferably, the through holes are provided in the vicinity of bottom portions of the ribs. This is effective to guide the cooling air to flow closely along the rib surface.
Preferably, an axial thickness of the receiving hole of the small-diameter fin is greater than that of another part of the small-diameter fin. The rigidity of the receiving holes of the small-diameter fin can be improved. Cracking of the fin and loosening of the diode can be surely prevented.